Alaska Age and Growth Precision Statistics

Statistics from 1990 to 2006.

Scientific Name

Common Name

Number Aged

Number Tested

Average Age

Anoplopoma fimbira Sablefish (Black cod)  35917 8052 10.4
Atheresthes evermanni Kamchatka flounder 120 24 8.93
Atheresthes stomias  Arrowtooth flounder  9761 2487 6.55
Gadus macrocephalus  Pacific cod 24057 7531 4.76
Glyptocephalus zachirus  Rex sole 2079 423 7.48
Hippoglossoides elassodon  Flathead sole 9713 2655 10.06
Hippoglossoides robustus  Bering flounder 237 48 8.61
Lepidopsetta bilineata Rock sole 7802 1698 8.39
Lepidopsetta bilineata Southern rock sole 482 101 10.16
Lepidopsetta peracuata  Northern rock sole 8559 2902 10.57
Limanda aspera Yellowfin sole 21046 5643 12.54
Merluccius productus  Pacific whiting 47916 14150 6.3
Microstomus pacificus  Dover sole 3601 848 18.53
Myoxocephalus polyacanthocephalus  Great sculpin 403 245 6.94
Pleurogrammus monopterygius Atka mackerel 22786 5435 4.07
Pleuronectes quadrituberculatus  Alaska plaice 3679 815 13.22
Reinhardtius hippoglossoides Greenland turbot 169 55 12.01
Sebastes aleutianus Rougheye rockfish 7234 2312 23.3
Sebastes alutus Pacific ocean perch 26189 8087 12.98
Sebastes ciliatus  Dark rockfish 1881 739 18.56
Sebastes polyspinis Northern rockfish 11994 2852 16.49
Sebastes variabilis  Dusky rockfish 4692 1186 13.37
Sebastes variegatus Harlequin rockfish 647 501 12.69
Sebastes zacentrus  Sharpchin rockfish 570 154 12.57
Theragra chalcogramma  Walleye pollock 202917 55282 6.35

 

Average age is the average of all fish aged. Unageable and ranged samples were excluded. Samples may have been collected several years before data was released. Rock sole (Lepidopsetta bilineata) statistics are from samples collected before the species was split into southern rock sole (Lepidopsetta bilineata) and northern rock sole (Lepidopsetta peracuata). 

Precision: Between-reader precision generally refers to the repeatability of an age when two different age readers age the same fish, with no knowledge of the other reader's age. For these twice-aged fish, an age is available from the reader (r) and a more experienced tester (t). Three measures of statistical precision can be calculated from the between-reader ages:

1.  Percent Agreement (PA): 

2. Average Percent Error (APE):  

3. Coefficient of Variation (CV): 

Where n = the number of fish in the test sample and is the average age of a single fish. 

APE and CV are averaged over all test samples. Often it is desirable to calculate PA, APE and CV broken down by age class. This is useful since precision estimates, especially PA, will vary with age. An advantage of both APE and CV is that they generally will not vary too much with age as they are scaled by

Kimura, D.K., and J.J. Lyons. 1991.  Between-reader bias and variability in the age-determination process. Fish. Bull., U.S. 89:53-60. 

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